An external defibrillator delivers energy to a heart of a patient via electrodes placed upon the patient's chest. External defibrillators are used to deliver energy in the form of a defibrillation shock to a heart that is undergoing ventricular fibrillation and has lost its ability to contract. Ventricular fibrillation is particularly life threatening because activity within the ventricles of the heart is so uncoordinated that virtually no pumping of blood takes place. If untreated, a patient suffering from fibrillation may die within a matter of minutes.
An electric shock delivered to a fibrillating heart may depolarize the heart and cause it to reestablish a normal sinus rhythm. In some cases, the patient may need multiple shocks, and the external defibrillator may deliver different quantities of energy with each defibrillation shock. Further, the defibrillator may provide additional or alternative therapies to the patient, such as cardioversion or pacing therapy. As examples, the external defibrillator may be an automated external defibrillator (AED) used by a first responder or bystander to treat the patient, or a more fully-featured defibrillator/monitor used by paramedics.